1. Field of the Invention
This invention relates generally to an integrated system for ion implantation and scrubbing treatment of the resulting ion implantation effluent for abatement of selected components therein, e.g., components which are hazardous or otherwise undesirable in the effluent stream discharged from the ion implant chamber.
2. Description of the Related Art
Ion implantation is progressively widely used for the introduction of dopant species into substrates for the manufacturing of semiconductor device structures.
The increasingly high levels of microelectronic device integration require shallow junction depths and low temperature process conditions, which are well accommodated by ion implantation. Ion implantation provides a high degree of control and reproducibility, and the ability to incorporate the dopant species into buried substrate regions of the microelectronic device structure.
Typical dopant species for silicon-based microelectronic applications include boron as a p-type dopant, and phosphorus, arsenic and antimony as n-type dopants. Silicon, germanium and oxygen are also used as dopant species in some applications. Dopant species are typically formed from source gases, such as boron trifluoride, arsine, boron trichloride, and phosphine, which entail significant safety and handling issues.
The dopant source gases are introduced to an ionizer where the high voltage arc discharges are employed to form a mixture of ionized species of the source gas. Magnetic field separation is employed for the subsequent separation of the specific ionic species to be implanted, which are then accelerated, focused and directed by a scanner mechanism in an ion beam onto the substrate to be implanted, to introduce the implant species into the crystal lattice of the substrate material being bombarded by the ion beam.
Ion implanters typically use BF3, AsH3 and PH3 as primary dopant gases. Other gases, such as SiF4, Ge4, etc. are also used.
Due to the hazardous character of these commonly used dopant gases, significant safety issues are raised. The dopant gases are supplied in conventional practice from high pressure gas cylinders. There is thus a substantial safety threat posed by the danger of leakage of the dopant source gas from the high pressure cylinder, or rupture of the cylinder in use.
The effluent from the ion implantation system thus contains the aforementioned source gases used in the specific application, as well as their ionization decomposition products. Due to their toxicity and hazardous character, it is generally desirable to scrub the effluent gas from the ion implant operation to remove such gases and decomposition products.
The effluent scrubbing operation can be carried out using a variety of wet and/or dry scrubbing operations.
Wet scrubbing of the effluent stream involves contacting the effluent gas from the ion implantation system with a scrubbing liquid to cause the undesired effluent stream components to be absorbed by the liquid, or to react with the liquid (e.g., a caustic solution for contacting with an acid gas effluent) to effect removal of the undesired components from the gas phase.
Dry scrubbing involves contacting the effluent gas with a solid material which functions to chemisorb or react with the undesired components to effect their removal.
In general, wet scrubbing requires the consumption of significant chemical reagents, and thus is less preferred than dry scrubbing, in which a bed of solid-phase scrubbing materials is employed, through which the ion implantation effluent gas is flowed.
It is important to note that for dry scrubbing purposes, the chemical requirements to scrub acid gases such as BF3 and SiF4 are entirely different than the chemical requirements to scrub hydride gases such as AsH3, PH3 and GeH4.
Available data show that BF3 passes through an ion implanter largely intact, PH3 is largely broken down to its elements while passing through the ion implanter, and AsH3 is broken down to a moderate level while passing through the implanter.
It is expected that other fluorinated acid gases will behave similarly to BF3 and pass through an ion implant system largely intact. Thus, the large flowrates of intact acid gas dopants mandate effluent stream treatment for removal of acid gases. While hydride source gases pass through only moderately intact, their high toxicity and low levels of permissible personnel exposure (for example, the threshold limit value (TLV) for AsH3 is 0.05 ppm, or a IDLH of 3 ppm) mandate abatement. Thus, the scrubber employed for treatment of the ion implantation system effluent gas must be capable of handling both acid gases and hydride gases. Such scope of scrubbing utility is difficult to achieve with a single dry scrubbing composition. Multiple beds of different dry scrubbing compositions, split beds of different dry scrubbing compositions, and dry scrubbing composition blends can be used, but these approaches all suffer from the deficiency of being cumbersome in their application and use.
In addition to the foregoing issues incident to the use and operation of ion implantation systems, empirical characterization of ion implant process exhaust streams reveal significant emissions of hazardous gases in the process system from source gas pumps, roughing pumps and from cryogenic pump regeneration cycles.
It would therefore be a significant advance in the art, and accordingly is an object of the present invention, to provide an ion implantation system which eliminates or at least ameliorates the aforementioned hazards of conventional ion implantation processes.
It is another object of the invention to provide an improved system for the treatment of ion implantation process effluents.
Other objects and advantages will be more fully apparent from the ensuing disclosure and appended claims.
The present invention relates generally to an ion implantation process system having an improved safety character relative to ion implantation process systems of the prior art.
In one aspect, the invention relates to an ion implantation process system, comprising a supply of source gas for the ion implantation process, joined in flow communication with an ion implanter apparatus, with the ion implanter apparatus discharging an effluent gas stream to an effluent abatement apparatus, for removing hazardous effluent species from the effluent gas stream.
The invention in a preferred embodiment includes an ion implantation process system in which the effluent abatement apparatus is positioned in the ion implanter apparatus as a unitary and integrated process arrangement.
In another embodiment, such integrated ion implantation process system further comprises the source gas supply in the integrated arrangement, with the source gas supply, ion implanter apparatus and the effluent abatement apparatus being in a unitary housing.
In accordance with another aspect of the invention, the ion implantation process system comprises one of the following feature sets:
features (a) and (b);
features (a) and (c);
features (a), (b) and (c);
feature (b); and
features (b) and (c).
of the features:
(a) the supply of source gas including a storage and dispensing vessel containing a physical sorbent medium having the source gas physically adsorbed thereon, with means for dispensing source gas from the vessel by desorbing source gas from the physical sorbent medium and discharging same from the vessel to the ion implanter apparatus;
(b) the effluent abatement apparatus including a dry scrubbing composition for contacting with the effluent gas stream to remove hazardous effluent species therefrom, in which the dry scrubbing composition is selected from the group consisting of the compositions:
(i) Fe2O3 
(ii) Fe2O3 impregnated with a base;
(iii) Ca(OH)2;
(iv) Ca(OH)2 impregnated with a base;
(v) Fe2O3 and MnOx, wherein x is from 1 to 2 inclusive;
(vi) Fe2O3 and MnOz impregnated with a base, wherein x is from 1 to 2 inclusive;
(vii) CuO and MnOx, wherein x is from 1 to 2 inclusive;
(viii) CuO and MnOz impregnated with a base, wherein x is from 1 to 2 inclusive;
(ix) CuO, Al2O3 and SiO2; and
(x) CuO, Al2O3 and SiO2 impregnated with a base;
wherein the base when present in the scrubbing composition is in a concentration sufficient to enhance the scrubbing capacity of the composition relative to a corresponding composition lacking the impregnated base component, with the base preferably being a strong base, such as KOH, NaOH, LiOH, BaOH, or the like; and
(c) the effluent abatement apparatus including at least one bed of a dry scrubbing composition through which the effluent gas stream is flowed to remove hazardous effluent species therefrom, and an end point monitor device operatively associated with each such bed, for determining when the scrubbing capacity of the bed is depleted to a predetermined extent.
As used herein, the scrubbing compositions herein disclosed are intended to be broadly construed, and may alternatively comprise, consist, or consist essentially of the specific stated components or ingredients hereafter specifically identified for such compositions. It will also be understood that such compositions may if desired be devoid of components or ingredients not herein expressly identified.
In a particular aspect, the ion implantation system of the invention may comprise as the aforementioned end point detector device (c) a quartz crystal microbalance arranged with a coating thereon with which an effluent gas stream component to be monitored is interactive to produce a change in frequency response thereof indicative of the end point operation of the bed of dry scrubber composition.
In another aspect of the invention, an ion implant system effluent stream is dry scrubbed to remove acid gas and hydride components thereof, using a dry scrubber composition consisting primarily of CuO and MnOx wherein x is from 1 to 2 inclusive, and wherein the composition contains from about 15 wt. % to about 40 wt. % CuO and from about 40 wt. % to about 60 wt. % MnOx, based on the total weight of the composition.
Other aspects, features and embodiments will be more fully apparent from the ensuing disclosure and appended claims.